Amplifier



July 4, 1933. G. L. BEERS AMPLIFIER Filed July 18, 1930 INVENTOR George Lfieers.

B ATi'ORNEY Patented July 4, 1933 FFE "- GEORGE L. BEERS, F "MERCHANTVILLE, NEW JERSEY, ASSIGNOR TO WESTINGHOUSE ELECTRIC MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA AMPLIFIER My invention relates to radio circuits and more particularly to specific improvements therein whereby a more economical operation thereof may be obtained.

During the functioning of a radio circuit, it is highly desirable to obtain a potential supply on the tube electrodes which, when once adjusted, will remain substantially constant andsubstantially uninfluenced by sudlo den changes in the potential source. In the present-day circuits, where the necessary po tentials are derived from an alternating-current-power source, substantially constant potentials on the tubesare difiicult to mainl5tain, as the frequent surges and potential variations occurring in the power system are passed on through the rectifying and filtering circuits associated with the receiving circuits and impressed on the tube electrodes,

resulting in output noises and injury to the tubes.

At the particular moments, when the potential impressed on the electrodes tends to take an upward'swing, if some means could be provided for diverting some of the energy which would normally pass through the tubes, it will become apparent that a more or less steady condition can be maintained with regard to the tube and its operation,

and the undesired results may be thus eliminated.

Likewise, conditions are encountered in mooern receivers, that employ negative bias for volume control and other similar expedients, which result in current variations in certain parts of the circuit. In such systems, the plate current of one or more tubes may vary through a range of 100 to 1. These variations in plate current are apt to aflect the voltages supplied to other tubes in the circuit.

In most power-supply systems, resistors are used to reduce the voltage for certain of the tubes which operate at potentials lower than the total rectified voltage. If a system of the character just mentioned is employed, and the plate current of, one or more of the tubes is caused to vary by changing the control grid bias, the voltages, as determined by the I. R. drop through the resistors, will Application filed July 18, 1930. Serial No. 468,876.

vary correspondingly. These variations in voltage may seriously afiect the operation of the receiver.

One of the most common of these variations occurs in the plate voltage of amplifier tubes when variable negative bias is used for volume control. As the negative bias is increased, thus reducing the plate current, the I. R. drop across the resistor through which the plate potential is applied to the tubes is decreased, with a resulting increase in the plate potential, thus tending to offset the effect of the increased bias. This increase in plate voltage may be of the order of seventy or eighty volts, in the usual receivers unless special precautions have been taken to avoid such changes.

Nith volume control of the usual manual type, this efiect is not serious except that the negative bias required to provide a given amount of volume control is greater than would be required with perfect regulation of the plate potential.

If automatic volume control is employed, however, this increase in plate voltage, with increase in negative bias becomes serious, as the amount of bias obtained from any given system, at any particular signal strength, is fixed, and an increase in plate voltage, therefore, reduces the effectiveness of the automatic volume control.

The usual method which has been used to correct this condition has been to connect a resistor from the plates of the amplifier tubes to their cathodes. The resistor used is of such value that the current flowing through it is usually greater than the current passing through the plate circuits of the tubes. In this way, the amount of variation in plate potential is greatly reduced. The objection to this method is that the current through the resistor serves no useful purpose other than to improve the voltage regulation of the device. Several watts are usually dissipated in this manner.

When a loudspeaker of the dynamic type is used in a radio receiving set, it is usually desirable to supply the field from the same power-supply unit which is used to operate the receiver. The plate potential applied to the output tube is usually at least twice that supplied to the radio-frequency or intermediate-frequency amplifier tubes. One of the requirements of an economical power-supply unit is to keep the total rectified current as low as possible. This result is accomplished, in my invention, by dividing the voltagesupply system in two parts which are connected in series, and supplying some of the tubes from one part of the system and others from the other part.

The loudspeaker field is connected across the extreme ends of the system, and a tap on the field winding connects to the cathodes of certain of the tubes. In this manner, the total rectified current supplied by the power-supply unitis kept at a minimum, and serious variations in plate and bias potcntials for the various tubes are prevented.

I have accomplished the above results in a manner which possesses great merit, in that my invention'is both extremely simple in its physical embodiment a nd very economical in its operation.

It is, accordingly, one object of my invention to provide a radio circuit substantially free from the influence of voltage changes in the potential-supply source.

Another object ofmy invention is to accomplish the above results without the addition of new elements to the circuit.

An additional object of my invention is to provide means for stabilizing the operation of the tubes in a radio circuit and, at the .same time, beneficially affect the operation of other apparatus in the circuit.

Another object of my invention is to provide a new combination and cooperation of elements in a circuit to obtain an economical operation of the same.

Additional features of my invention will be disclosed in the following description, taken in conjunction with the accompanying drawing wherein the single figure represents the preferred adaptation of my invention, as applied to a superheterodyne circuit.

Referring particularly to the drawing, the circuit disclosed therein comprises briefly an antenna circuit 1 coupled to a stage of radiofrequency amplification 3 through a bandpass filter apparatus 5 for selective tuning. The amplified radio signals in the output circuit 7 of the radio-frequency amplifier are impressed upon the input circuit 9 of the first detector stage 11 wherein they are caused to beat with oscillatory current from an oscillation generator 13 to produce beat notes at intermediate frequency which are amplified through thetwo stages 15 and 19 of intermediate-frequency amplification. The output circuit 17 of the last intermediate-frequency stage is inductively or otherwise coupled to a second detector stage 21 wherein the signals at intermediate frequency are transformed into signals at audio frequency. The audio-frequency signals are then amplified by the stage of push-pull amplification 23, the output circuit 25 of which supplies the voice coil 27 of a speaker 29 of the dynamic type with the audio-frequency current necessary to its operation.

Automatic volume control for the system is provided, comprising a thermionic device 31, the grid of which influenced by the same signal potenials as the grid of the detector tube 21. In the anode circuit of the control tube are a pair of resistors 33 and 35, both of which comprise grid-bias elements in the input circuit 37 of the radio-frequency stage of amplification 3, and one of them also comprises grid-biasing means for the intermediate-frequency amplifiers 15 and 19. This volume control means functions to maintain a substantially uniform volume level in the system in spite of changes in signal intensity. The circuits involved and the manner of operation are more fully described in a copending application of mine, Serial No. asses, filed May 1, 1930.

A source of operating potentials for the various thermionic devices in the system comprises a voltage divider 39 which is shunted across the output terminals of a socket power unit 41 comprising a rectifier and filter system inductively coupled to a source of alternating current.

Filament current for the push-pull amplifier tubes is provided for by a coil 43 inductively coupled to the source of alternatingcurrent supply and, in like manner, current is supplied to the heaters of the other tubes, which are illustrated as being of the heater type, from a coil 15 also coupled to the source of alternating current.

One of the novel features of my invention, as pointed out above, resides in means for economically operating a system of the type described, this result being obtined through an improved arrangement and cooperation of elements. 7

Instead of obtaining potentials from the voltage divider 39 by a more or less parallel connection of the thermionic devices to the divider, as is the common practice, I have found that, by connecting certain of the tubes to one portion and others of the tubes to another portion of the divider, both portions of the divider being in series, less rectified current is necessary for the successful operation of the system.

Referring more particularly to the draning, the first detector 11, the oscillator 13 and the volume-control tube 31, all obtain their potential supply from the lower half of the voltage divider 39, whereas, the radio-frequency amplifier 3, the intermediate-frequency amplifiers 15 and 19, and the second detector 21 obtain their potentials from the upper half of the divider. My invention is not limited to the above arrangement, as any particular grouping of the thermionic devices may be resorted to, so long as certain of them are supplied from one portion of the divider and others from another portion. In fact, economy in the construction of the potential supply system may be obtained by designing it for a voltage sufficient to span a series connection of all the plate circuits of the tubes, as the current necessary then would be materially reduced, permitting a saving in cost of apparatus.

To the anodes of the radio and intermediatefrequency amplifiers and the second detector, I connect the high-potential end of the field coil 49 of the dynamic speaker 29, the low-potential end being connected to the lowpotential side of the voltage-supply source. A tap 51 on the mid-point of the field coil 49 is connected to a point 53 on the voltage divider 39 intermediate its ends, in the specific instance disclosed in the drawing, this intermediate point being the cathode connection for the intermediate-frequency stages. By connecting the center tap of the coil, as described, regulation of the voltage supply to both sets of tubes is greatly improved, as each half of the coil will act to bypass or shunt certain of the spacedischarge-current paths of the tubes and will, therefore, function in the nature of the bleeder resistors, referred to as constituting prior art.

lVhile I have referred to the coil sections as shunting certain of the space-dischargecurrent paths, they might also be considered as shunting the voltage divider 39, in which case, it may be said that the coil 49 will function to maintain substantially constant potentials across this part of the system. If sufficient taps were provided on the field coil of the loud speaker or energy-transferring device at appropriate places, the voltage divider may be dispensed with entirely.

Under any condition, the current shunted through the field coil is not wasted, as when separate bleeder resistors are used, but, on the contrary, this current is put to good use in providing field excitationfor the energytranslator device 29.

It will be obvious, therefore, that I have disclosed a system capable of fulfilling the objects of my invention, without the addition of new elements to the circuit. I have thus provided means for stabilizing the operation of the tubes and, in addition thereto, have ob tained field excitation for the loudspeaker.

It will be apparent that my invention is not limited, in its operation, to a circuit of the superheterodynetype, as illustrated, but may be adapted to any circuit wherein unidirectional potentials are used, regardless of the source of said potentials, whether they be obtained from a rectifying and filtering circuit, as shown, or from a battery or directcurrent generator etc.

Various modifications also may be suggested as falling within the scope of my invention. The field coil of the loudspeaker may, for example, be connected in series with the voltage-divider element. While, in this position, it may not eificiently function as a voltage stabilizer, it will obtain its magnetizing current from the plate-current supply. Because of the reduced amount of plate current which will be necessary for operation of the system, suitable adjustment may be made in the number of turns of the coil to provide the correct value of ampere turns in the coil. Any other apparatus in the system capable of being used in the same manner as I have disclosed in regard to the field coil of the loudspeaker, may, of course, be substituted for the coil shown.

I desire, therefore, not to be limited to the specific details of my disclosure, except insofar as is necessitated by the prior art and the appended claims.

I claim as my invention:

1. In combination, an apparatus comprising a plurality of electron discharge devices and a source of potential for said devices, certain of said devices being connected to derive potentials from one portion of said source and others of said devices being connected to obtain potentials from a separate portion of said source, an impedance coil in shunt with certain of said devices, said impedance comprising an element of aloud speaker device.

2. In combination, an apparatus comprising a plurality of electron discharge devices and a source of potential for said devices, certain of said thermionic devices being connected to derive potentials from one portion of said source and others of said devices being connected to derive potentials from an other portion of said source, both portions being serially connected, an impedance shunting one group of said electron discharge devices, said impedance constituting an element of a loud speaker device.

3. In combination, an apparatus comprising a plurality of electron discharge devices and a source. of potential for said devices including a voltage divider, certain of said discharge devices being connected to derive potentials from one portion of said divider and others of said devices being connected to obtain potentials from another portion of said divider, an impedance in shunt relationship to said divider and a connection from the mid-point of said impedance to a point on said divider intermediate its eX- tremities.

4:. In combination, an apparatus comprising a plurality of electron devices, a source of potential for said devices including a voltage divider, certain of said devices being connected to derive potentials from one portion of said divider, others of said devices series connection across a portion of said divider, and an impedance shunting a portion of said divider in parallel with the output circuit of one of said devices, said impedance constituting an element of a loud speaker. V

In testimony whereof I have hereunto subscribed my name this sixteenth clay of June GEORGE L. BEERS. 

